Current methods of placement and positioning of coils for Transcranial Magnetic Stimulation (TMS) studies are either manual methods or approaches designed for research that require expensive and complex imaging or computational systems to determine three dimensional spatial coordinates for positioning reference. These techniques have severe clinical limitations. The manual methods do not provide a convenient means for repeated and accurate placement, while the three dimensional spatial methods based on imaging modalities are expensive, time consuming, and not conducive to clinical use. A positioning technique for clinical use is desired that provides a simple way for the operator to perform repeated and accurate coil placement for TMS studies and treatments in a time-efficient and inexpensive manner.
Manual Methods
In accordance with the conventional manual placement and position marking technique, a treatment position on the patient's head or a position used to find a treatment position, such as the patient's motor threshold position (MTP), is determined by moving the coil near a predicted area determined by patient anatomical landmarks until the desired motor response is achieved. The position is marked, for example, with an ink mark on the patient's head. In the case of using the TMS coil for treatment of depression, for example, the TMS therapy position is determined by moving the coil from the MTP along a line in the anterior direction a prescribed distance (a widely accepted distance is 5 cm). The Therapy Position (TXP) is then marked on the patient (e.g., with ink) so it can be easily found in subsequent therapy sessions.
The most common method of localization used for TMS studies is described by George et al. in “Daily Repetitive Transcranial Magnetic Stimulation (rTMS) Improves Mood in Depression,” NeuroReport, Vol. 6, No. 14, October 1995, pp. 1853-1856, and by Pascual-Leone et al. in “Rapid-Rate Transcranial Magnetic Stimulation of Left Dorsolateral Prefrontal Cortex in Drug-Resistant Depression,” The Lancet, Vol. 348, Jul. 27, 1996, pp. 233-237. Simply stated, in these methods the coil is first moved over the area of the left motor cortex until stimulation of the contralateral abductor pollicis brevis muscle (APB) is attained. This position is the motor threshold position (MTP) and is typically located on a line between the left auditory meatus (i.e. ear canal) and the vertex of the head, at a point about ½ to ⅔ of the distance to the vertex. In the case of excitatory stimulation of the left prefrontal cortex for the treatment of depression, for example, the TXP is located by starting at the MTP and moving 5 cm toward the midpoint between the tip of the nose and the nasion (protuberance just above the bridge of the nose). More details of techniques for determining the MTP are also described in U.S. Pat. No. 7,104,947, the contents of which are incorporated herein by reference.
The shortcomings of such manual methods are that precisely determining the line from the MTP to the TXP is difficult, marks applied to the patient that can wash off between treatment sessions are cosmetically undesirable, the coil may not be comfortably held at the TXP throughout a therapy session, and the technique is highly operator dependent and not conducive to repeatable and accurate positioning.
The problem of applying marks to the patient has been addressed in the art by applying a swim cap or similar conformal headgear to the patient and marking the headgear rather than the patient. Of course, this approach requires careful registration of the headgear during subsequent therapy sessions, which is crude, imprecise, and highly operator dependent. Moreover, such an approach still requires accurate coil placement and a mechanism for holding the coil in place.
Complex Imaging/Computational Systems
The Brainsight™ System developed by Rogue Research, Inc. of Montreal, Canada and distributed by Magstim is complex and is designed primarily for research purposes. This system uses diagnostic images from MRI or PET systems to determine the spatial relationship between internal anatomy and external landmarks and then aligns to the external landmark for therapy or other studies requiring accurate localization. While this approach is useful for research purposes, it is highly impractical and complex and is thus not usable in general clinical practice. Moreover, such techniques have generally been used to overlay coordinate systems onto images and not for identifying particular treatment positions for specific therapies.
Robotic Arms for Holding TMS Coils
U.S. Pat. Nos. 6,266,556 and 7,087,008 include descriptions of methods in which a robotic arm is operatively coupled to the TMS coil for positioning the coil with respect to the patient and holding the coil in place during TMS treatment. A similar technique using a robotic arm for coil placement is also disclosed in U.S. Pat. Nos. 6,827,681 and 6,830,544. These patents further disclose a technique for modeling the spatial structure of the patient's brain for determining the proper stimulation position using a stimulation model. While these techniques provide controlled movement and placement of the coil, they are quite expensive and do not provide for repeatable placement of the coil with respect to a particular patient's head in a clinical setting. As a result, the manual and/or complex imaging techniques described above must also be used for placement of the coil with respect to the patient.
Positioning TMS Coils Relative to Fixed Head Position
U.S. Patent Publication No. 2005/0148808 to the present assignee describes a TMS coil positioning system in which the patient's head is fixed and the TMS coil is fixed at a treatment position in the coordinate system of the patient's head. The position in the coordinate system is recorded for use in subsequent clinical sessions. In an exemplary embodiment, the positioner assembly is a mechanical system that supports the weight of the TMS coil and allows the operator to freely move the TMS coil to search for the treatment position and/or the patient's motor threshold position (MTP). Once the MTP is determined, the positioner assembly requires a single adjustment of the magnet position to locate the treatment position (TXP) where the coil is locked in place for the duration of the TMS therapy. By recording the positions of the different adjustable components in the respective coordinate directions of the coordinate system of the patient's head, exact repositioning of the TMS coil for the patient during a subsequent clinical visit is made possible without use of expensive imaging equipment.
The apparatus includes three basic components including (1) a headset assembly that accepts the patient's head and fixes its position, (2) a coil positioner assembly that accepts the headset assembly and holds the headset assembly and the patient's head at a fixed position, controls positioning of the TMS coil within a coordinate system defined about the fixed position, and holds the TMS coil in place at a treatment position during treatment, and (3) an alignment strip applied at a position in registration with an anatomical landmark of the patient including at least one registration mark for aligning the patient's head within the headset assembly. Each of these components working together permit the coil assembly to be located in coordinates with respect to the patient's head such that the treatment may be repeated during a subsequent visit by repeating the coordinates. However, such a system requires the treatment coil to be affixed to the positioning apparatus and the patient's head to remain fixed relative to the apparatus during treatment. A coil positioning system and treatment apparatus is desired that physically separates the functions of supporting the weight of the coil from the alignment function so that the coil can be easily placed or removed and so that the patient can be situated in a range of positions, thereby increasing the patient's comfort and acceptance of the TMS treatment.
Thus, the need for a simple, cost-effective and intuitive way to accurately and repeatably position the coil for TMS therapy in a clinical setting without fixing the patient in one position during treatment has not been met in the prior art. The present invention addresses this need.